Traditional water heater tanks are steel tanks lined with glass or are made of some suitable plastic or fiberglass material. These glass lined steel water heater tanks are typically formed in complicated manufacturing processes where the heads, bases and tank shells are formed separately, the heads are press-fitted in and welded to the tank shells, glass enamel applied to the tank shell and head as a bisque and then baked at a temperature of from 1600.degree. to 1750.degree. F. in order to melt the glass and coat the steel. Enamel is then applied to the base and the base is pressed into the shell and welded thereto.
However, during the welding of the base to the shell, the glass lining typically reflows and deposits glass in the weld between the shell and the base which reduces the amount of glass coating at the seam formed by the juncture of the base and the shell and weakens the weld. Because of these problems, these water heater tanks typically fail along the juncture formed by the shell and the base because of the reduced protection of the thinner glass lining at this point and because the weld joining the shell and the base is generally weaker than the other welds in the water heater tank because of the glass contained therein.
Attempts to combat corrosion in these typical glass lined steel heater tanks have included the placing of a sacrificial magnesium anode within the tank in order that the magnesium anode would dissolve and coat any exposed steel surface in the tank with a magnesium oxide coating. However, this method of preventing corrosion has had problems in that the steel in the water heater tank may be attacked by the water and chemicals contained in the water before an adequate protective coating of magnesium oxide is formed thereon. Another problem is that the amount of protection available for any exposed steel surface is dependent on the amount of magnesium used as a sacrificial anode. After the sacrificial anode is consumed, there is no protection available for any subsequently exposed steel surfaces.
Plastic or fiberglass water heater tanks do not have the problems of corrosion that are commonly found in glass lined steel water heater tanks but are not capable of being gas-fired because of the temperature limitations associated with the materials of their construction and involve complicated molding procedures in their fabrication.
Therefore, the need exists for a water heater tank that can be easily fabricated, provides maximum corrosion protection and is flexible enough to employ various heating elements such as a gas burner or electrical resistance heating elements as the means of heating the water.